Putting paralyzed people back on their feet has long been the dream of Dr. E. Byron Marsolais, a surgeon at the Cleveland VA Hospital. There, scientists are working to stimulate the nerves that control muscles using electricity, a technique called Functional Electrical Stimulation (FES). The experimental trials are tough going for participants, but for the pioneers in this ambitious effort, the struggles may be worth it, as they strive toward their goals of becoming more mobile.

When spinal nerve fibers are injured, electrical signals from the brain do not reach the motor nerves that control the muscles. In Functional Electrical Stimulation (FES), a tiny wave of electricity sent by electrodes implanted in the paralyzed limb makes the muscles contract. As you see on Frontiers, a computer wired to the electrodes is programmed to stimulate leg muscles to move in the correct sequence.

Muscle action occurs within a sarcomere, made mainly of overlapping filaments: a thick protein, myosin, and a thinner protein, actin. Segments of sarcomeres are located next to each other along the length of the muscle.

Materials:

2 colors of clay

video camera

tripod

lights

NOTE: If a camcorder is not available, animate muscle action by making a flip book.

Objective:

By modeling a sarcomere's action, you will gain a kinesthetic and visual understanding of muscle contraction.

Procedure:

NOTE: Please refer to the illustration for this activity.

Figure A illustrates a sarcomere in its most relaxed state. During muscular contraction, the actin filaments slide inward (B & C). Eventually, the filaments completely overlap and begin to buckle (D). When the muscle relaxes, the actin filaments slide back across the myosin. Exercise stimulates the production of myosin and actin.

Using two colors of clay, make a "sandwich" of actin and myosin layers.

Arrange the clay filaments to represent the sarcomere in its most relaxed stage (Figure A).

Set up a camcorder on a tripod and capture several frames of this model.

Carefully slide the actin filaments inward by a few centimeters. Keep everything else, including the camcorder, the same. Take several more frames. (A single-frame camcorder would obtain the smoothest results, but others will work. Or, use a Super 8.)

Continue animating and videotaping the model until the actin filaments have buckled in the center of the sarcomere. Then play back your video to see the process on film; reverse to see "unbuckling."

Scientific American Frontiers
Fall 1990 to Spring 2000
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